The original flea market may be the Marché aux puces
("market with fleas" in French) of

Saint-Ouen, Seine-Saint-Denis, in the northern suburbs of Paris.
It is a large, long-established outdoor bazaar, one of four in Paris.
From the late 17th century, the makeshift open-air market in the town of
Saint-Ouen began as temporary stalls and benches among the fields and
market gardens where ragpickers exchanged their findings for a small
sum.

Some television shows focus on the appraisal of second hand goods often
found at flea markets that are worth far more than the buyer paid. The
most popular of these shows is Antiques Roadshow in the United Kingdom,
which led to American, Canadian, Swedish and Dutch versions of the show.